A ring type current sensors use a right-hand rule. As disclosed in JP-2003-167009-A2 for example, the ring type current sensor includes a C-shaped core which provides a magnetic path therein and a magnetic field sensor such as a Hall effect sensing device disposed in a gap formed between both end faces in a circumferential direction of the core. The ring current sensor detects a magnitude of a current flowing through a conductor such as a bus bar passing through the core.
The magnitude of current flowing in the conductor is directly proportional to the magnetic flux density in the magnetic path including the gap. The magnetic field sensor outputs a voltage proportional to the magnitude of the magnetic flux density in the gap. Thus, an output voltage of the magnetic field sensor indicates the magnitude of the current flowing in the conductor.
A conventional ring type current sensor such as that shown in FIG. 7 has a C-shaped core 101 disposed to surround a current conductor or a bus bar 3 and having a constant cross-sectional area in a direction perpendicular to the magnetic flux passing therethrough. This sensor causes a magnetic flux concentration at a portion 112 opposite to a gap 102 in a diametrical direction of the core 101, that is, at the intermediate portion between two opposing end faces 111 in the circumferential direction of the core 101. The magnetic flux concentration is especially prominent at a radially inner side of the portion 112. The magnetic flux concentration increases a magnetic hysteresis at this portion 112.
Especially in a ring type current sensor 4 for detecting a large current magnitude, the magnetic hysteresis spoils the proportional relation between the actual current and the output voltage of the magnetic sensor. The core 101 made of a magnetic material having a relatively small magnetic hysteresis can restrict this drawback. This kind of magnetic material however increases a manufacturing cost of the ring type current sensor.